Expulsion gap lightning arrester



Patented Nov. 25, 1952 nxroLsfon GAP LIGHTNING ARRESTER 'ra'usias IrvenEldridge, Jr., Brooklin'e, and WaljtcrH'. Yung, (}lenside, Pa.,assignors to Electric y s'ervice Manufacturing Company, Philadelphia,Pa.,a corporation of Pennsylvania A pii'mt'ibii caster 1, 1948, SerialNo. 52,318

4 Claims. (01. 313 -231) Our invention is an electrical protectivedevice or lightning arrester providing a substantially unimpeded pathfrom an electric circuit or equipment to ground for lightning orothertransient, high potential, electric disturbances, and which quicklysuppresses arcs maintained by follow current aeross gaps ionized by ahigh potential discharge in passing to ground.

In its preferred form, our invention comprises a series of telescoped,cylindrical walls of gas forming material having. spaces between themforming multiple, parallel, cylindrical arc slots of narrowcross-section but extensive area. Each slot is bounded laterally byconcentrically curved spaced walls, and hence has, in transversecrosssection the shape of a narrow rectangular slot bent around andspaced from an axis. These parallel slots are intersected by areelectrodes which are connected, mediately or immediately, with line andground. Preferably, the walls form ing the constricted arc slots, andthe electrodes intersecting such slots, are enclosed. in a nonconductinghousing, which also encloses electrodes forming an isolating gap betweenline and a proximate electrode intersecting the arc slots. The isolatinggap prevents application of line voltage to thearc-suppress'ing elementsof the arrester except during acutal discharge to ground, and anysurface leakage 'orcreep-age is over the housing and not through the'arrester -elements. The enclosure of the isolating gap within thehousing prevents any fouling of the gap which, if it occurred, wouldallow the application of line current to and deterioration of the wallsof the arc slots. b

The walls forming th arc slots are; preferably reinforced by anencircling steel sleeve having its end nearest the isolating gap beveledor flared outward and preferably coated, wholly or partly, withinsulation to prevent fiash over to the sleeve from the proximateisolating gap elec- 'rode'd uring a discharge to ground; I

The concentric cylindrical arc slots are preferably of unequal lengths,the slot of smaller cross-sectional area being the shorter. This tendsto divert impulses of steep wave fronts to the outer and longer arc slotand to divert heavy currents of slower rising steepness to the inner,shorter arc slot, and the'multiple slots permit the use of wallstherefor having gas generating areas magnitudes of very high orderbecause of the multiple paths principle. v I

The gas generating surfaces of the arc slots are preferably composed ofhard fibreor horn fibre, but may be composed of or contain othersuitable gas generating substances, such as boric acid, activated by anarc to produce de-ionizing gases tending to suppress an arc.

The principles of our invention, and the best mode in which we havecontemplated applying such principles will further appear from thefollowing description and the accompanying drawings illustrating 'apreferred embodiment of my invention. v

In the drawings, Fig, 1 isja longitudinal sectional view of a lightningarrester or protective device embodying ourinvention; Fig. 2 is atransverse sectional view taken on the line 22 of Fig. 1 Fig.3 is atransverse sectional view taken on the line 3-3 of Fig. 1; Fig. i is anenlarged broken perspectiveview of the ground electrode at the bottom ofthe arc slots; Fig. 5 is an exploded, longitudinal sectional View of theelectrode shown in Fig. 4 and of the core and tube to be seated therein;Fig. 6 is a transverse sectional view taken on the line G6 of Fig. 5;and Fig. 7 is a fragmentary part sectional view illustrating amodification of the flaring and coating ofthe top of the reenforcingsleeve. 7

The embodiment of our invention illustrated'in the drawings comprises anexternal housing composed of a cylindrical, wet-process porcelain body Ihaving one end closed by a porcelain plug 2 glazed into the body. Theopposite end of the housing is countersunk to form a seat 3 for theflangededge ll of a conducting cup 5 which may be provided with a hollowdepending terminal boss 6 for the atachment of a ground I. The cup 5 issecured against the seat 3 by a plastic seal 8 and non-plasticcement 9.

A cylindrical hard fibre shell 13 has its end threaded into the threadedcup 5 and is encircled by .a steel, seamless, reinforcing sleeve orshield ll which may be staked to the cup 5 and is therethrough connectedto the ground. The sleeve H projects along the shell Ill beyond theportion thereof containing the arc quenching slots and upper arcelectrode hereinafter described. H v

As illustrated in Fig. 1, the upper end of the sleeve ii is flaredoutward by belling the rim 52 thereof to form a channel which maybefilled with a ring of non-conducting sealing material l3, such as'resin.In the'modifica'tion illustrated in Fig. 7, the upper end of the sleeveH is flared by beveling the edge 12' which may be surrounded by anon-conducting ring I3. The fiaring of the upper end of the sleeve Haway from the tube It greatly decreases the liability to flashover.

A cylindrical electrode H2- is seated in the cup 5 within the shell land has a peripherial wall 55 containing the countersink It at one endthereof and diametral slots I? which communicate, through an aperture 19in the bottom of the electrode, with a discharge passage 20 through theterminal boss 3.

A core 2| is seated on a non-elastic metallic washer 22 in thecountersink IE; the core preferably consisting of a filler rod 23 and afibre tube 24.

A fibre tube 25 is telescoped over the core 2! and spaced slightlytherefrom and from the inner wall of the shell [0 to form multiple,concentric, cylindrical arc slots each having walls of gas-formingmaterial concentric with but spaced from one another.

The are slots are intersected, at the upper ends thereof, by anelectrode 26 making a close fit with the inner wall of the shell l0intermediate the ends thereof. The electrode 23 has a peripherial flange2? closely encircling and centering the reduced upper end of the tube25. An elastic gasket 28 and a felt gasket 29 are interposed between theend of the tube 25 and the electrode 26 and lie in a channel between theflange 21 and boss 30 of the electrode. The boss 30 extends into the endof the tube 25 and presses against the top of the core 2! to press ittightly against the washer 22. The electrode 26 may be secured to thecore 2| by a screw 3|.

The head of the screw 3| is housed within a conducting tube 32 which istelescoped over the boss 33 on the top of the electrode 26.

A conducting plug 35 is threaded into the upper end of the shell II),with its periphery well inward from the periphery of the tube [0, andhas a boss 35 extending into the tube 32. By tightening up the plug asin the shell ID, a desired degree of pressure may be applied to theelectrode 23, tube 25, core 2! and electrode 14 to prevent axial orrotary movement of these parts and secure their concentricity to oneanother.

An electrode 36, seated in the plug 34, and an electrode 37, carried bythe end closure 2, form an isolating gap 33 normally isolating the arequenching elements of the arrester from line but providing a path toground for impulse surges due to lightning or the like.

The electrode 31 has a shank 39 which passes through an aperture 42 inthe closure 2 and the joint between the shank and closure is sealed bythe fibre gasket 40 and 4| which are squeezed by the electrode 31 andgasket cup 43 when the nut 34 is drawn up on the shank 39. The nut 44may be provided with a serrated surface complementary to the wire clamp45 for gripping the line conductor 46 when the nut 41 is tightened up. Ahollow cap 48 is detachably connected with the shank 39 to provide aweather shield for the line connection assembly.

The interior of the housing I is ventilated through ventilatingapertures 49 through the fiange 4 and the cement 9.

The arrester may be mounted in any suitable position adjacent to acircuit to be protected by a metal bracket 50 encircling the housing Iintermediate the ends of the reinforced sleeve II; the bracket 50 beingspaced from the line terminal of the arrester by the corrugated area ofthe surface of the housing I.

When a lightning surge or other transient high potential electricdisturbance reaches the section of the line with which the line terminal39 is connected through the conductor 46, it is discharged across theisolating gap 38, through the electrode 36, plug 34, conductor 32,electrode 26, through one or both of the arc slots, electrode l4,terminal boss 6 and conductor 1 to ground. The are through the arc slotsquickly generates large volumes of de-ionizing gas which extinguishesthe arc maintained by follow current at or before the next zero point ofthe cycle of the alternating dynamic current. The generated gas isexpelled from the arc slots through the electrode slots l1 and passages19 and 20, away from the ground conductor 1.

An arrester constructed in accordance with our invention has a lowimpulse spark-over voltage, a high discharge current capacity and a highdynamic failure voltage and are suppressive characteristics. Understandard test conditions, our arrester will cut ofi flow of 60 cycledynamic follow current to ground within approximately an eighth of acycle after the inception of a breakdown due to surge current, and willdischarge without appreciable damage to itself test current of very highmagnitudes, e. g. of the order of 180,000 amperes, and restore itself toits original operating condition. 7

The area of gas generating material is large proportionately to thelength or volume of the arc slots and the arc is so distributed betweenthe parallel slots that impairment of the walls of the slots isminimized. The impulse breakdown is inherently low and is furtherlowered by the conductive connection of the steel shield H to ground andconsequent balancing which is accomplished by the capacitances betweenline and ground terminals.

Having described my invention, I claim:

1. An electrical protective device comprising a non-conducting externalhousing, a conducting cup seated in one end of said housing, a tubularshell seated in said cup, a reinforcing metallic sleeve encircling saidshell and having one end secured to said cup and its other end flared,an electrode seated in said cup within said shell and having anapertured rim and a central socket, a core seated in said socket, a tubesupported by the rim of said electrode and encircling said core, saidcore, tube and shell forming multiple concentric cylindrical arc slotshaving walls of material that generates gas in the presence of an arcand are concentric with but spaced from one another, an electrodeintersecting said arc slots and having a boss engaging said core and ahead engaging said tube, a conductor connected with said last namedelectrode, a plug threaded in said shell against said conductor andpressing said core, tube and electrodes axially, said plug having amember forming an electrode, a closure for the other end of saidnon-conducting housing, and an electrode carried by said closure andforming an isolating gap with said electrode last named.

2. An electrical protective device comprising a non-conducting externalhousing, a tubular shell within said housing and having an electrodeintermediate the ends thereof and an electrode at each end thereof, aconducting member connecting the intermediate electrode with one of theend electrodes, a core and a tube interposed between the intermediateelectrode and the other end electrode and forming with said shellparallel concentric cylindrical arc slots each having walls of materialthat generates gas in the presonce of an arc and are concentric with butspaced from one another, and an electrode at one end of the housing andcomplementary to the first named electrode at an end of said shell andforming therewith an isolating gap.

3. An electrical protective device comprisin a conducting cup, a tubularshell seated in said cup, an electrode at each end of said shell and anelectrode intermediate the ends of said shell, a reinforcing metallicsleeve encircling said shell and conductively connected with said cupand having its end remote from said cup flared outwardly, a core and atube within said shell between said intermediate electrode and one endelectrode, said core, tube and shell formin parallel cylindrical arcslots each having Walls of materialthat generates gas in the presence ofan arc and spaced from one another, and a conductor within said shelland mechanically spacing and electrically connecting said intermediateelectrode and the other of said end electrodes.

4. An electrical protective device comprisin a hollow tubular shell ofinsulating material, an electrode seated in one end of said shell andhaving a peripherial wall countersunk at one end and diametral slotscommunicating with an axial gas venting passage through the other end.of said electrode, a core seated in the countersunk end of saidelectrode, a tube seated on the slotted end of the peripherial wall ofthe electrode, said core and tube forming an arc slot having walls ofgas forming material spaced from one another, and an electrodeintersecting said are slot at the end of said core and tube remote fromsaid first electrode to support said core and tube in concentricrelation, said slots and axial passage providing an escape path forgases resulting from an arc between said electrodes in said are slot.

T. IRVEN ELDRIDGE, JR,

WALTER H. YOUNG.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,923,748 Roman Aug. 22, 19332,050,397 Torok Aug. 11, 1936 2,170,337 Pittman et a1 Aug. 22, 19392,285,198 Fitger June 2, 1942 2,330,918 Pittman Oct. 5, 1943 2,332,399Pittman Oct. 19, 1943 2,338,479 Ackermann Jan. 4, 1944 2,414,308 KalbJan. 14, 1947 FOREIGN PATENTS Number Country Date 528,895 Great BritainNov. 8, 1940

